Battery Vehicle Society

I am sure you are aware, but any fuses, switches, circuit breakers, relays etc., rated for AC voltage will need to be derated when used on DC voltages. Better yet use parts that also list their DC ratings as well as the AC ratings.

Granny & eggs comes to mind
The Ampere levels will be too low and physically too big for mains fuses. The biggest issue is Earth leaks on EV's.

RCD's,

Going back to original thread, I thought I should share my recent experience with a Valence Battery. The first pic shows the internals of a X27 130ah 12+ v battery pack. Its made up of a set of 11x9 parallell 4 Series to make the voltage and current.
I had one that rested at about 10+v (Others had nicely recovered to just over 13) so attached a simple 4a charger that had worked well on the others.
Next day I smelt an awful smell when entering my workshop, then saw the remains of the battery. I guess one layer of the 11x9 had a shorted cell hence the 10+v, with charging this just heated up taking out others etc. Fortunately they are supposed to be amongst the safest in term s of not burning, but it obviously got vey hot and a lot of the cells blew apart.
Very messy. I do consider myself lucky.
Not sure how I feel about using these, I had got a price from them of some old model batteries that were less than half price, still a lot of cash though.
Note the careful placement of an old Drum of Polyester resin in the internal shot. Thankfully no where near the one that went Phut.

Grumpy-b

Sorry to see that.
So the BMS did not work!
A 4A charger, No fuse?.. A sensible voltage on the battery charger would be pointless here.

The trouble is, you had a pack at 10.1V. This means one string (3.2V, 130AH) of the 13.3V four is completely dead and unrecoverable. Recharging makes dead cells hot. Seems the BMS does not take temperature into account.

To kill a cell, it gets discharged then driving the stronger cells to force it into a reverse charge. They get mad hot no matter which way the load is applied from there on. This is easy with top balanced cells as the weakest of the string hits zero first, dies and becomes a dummy load while the BMS (always pathetically) attempts to balance the others down creating more heat!

I'm totally of the Jack Rickard school of Li cells and this simply defines exactly everything he's said

Wow, lucky escape, it could have been far worse. I am guessing that by using the 4amp charger you had effectively bypassed the bms. If this is the case then it again shows the importance of individual cell monitoring while charging. Thanks for sharing the pictures, when I started the thread I hadn't envisaged it becoming a showcase for our screw ups, but hey, that is fine with me.

A real bms would have a contactor that released the pack if anything got too hot, cold or to high, too low a voltage.

No car manufacturer I know of apart from the GM Volt/Ampera and the Karma Fisk have cell level monitoring. They both have odd ones that burned to the ground. One was a Volt charging during a thundery night. The Karma's A123 pack is still under investigation but we know about the faulty spot welder issue on the A123 facility . Which will do exactly the same as we see above.

Only after the insurance pays is the truth found.

Bottom balancing and never overcharge has never lost a pack yet. - This is from a man who abuses cells like a fetish.

The cells do have some inbuilt control , but not a proper BMS. Although they are sold as a replacement for 12v batteries hence their form factor which expressly mimics a 12v Lead Acid battery.
They were charged directly from a simple power source which, since they were so low in voltage / power would not have over cooked them. Interestingly even with a BMS, if one cell had internally shorted, i doubt if anything would have been simply detected. Since the pack was not over voltaged, curent was really very low.

Still something to put down to experience.
VAlence have been really helpful, I had previously been in contact with them about buying some of these. They rightly point out the importance of proper BMS etc . Personally I think that this shows what an excellent and safe product the Valence chemistry is when experiencing any failure.

Grumpy-b

There's a reason to everything and not seeing it will only make it happen again.
For sure I'd be very wary about one of those makes now. When a good cell should be good for over 1,500 80% cycles to lose 20% of charge... Something was very wrong with their product to lose a 130A chain in a place it was designed to work in.

If that pack did not have cell level monitoring, I'll eat my hat.

I'm sorry for being such a pedant or plain anal about this but if a guy wrecks cells with no bms. Fair enough. With a bms? No excuse.

I fully accept all responsibility for this, however a low current on a low pack, not even attempting to get near the battery capacity. should have been safe even with no BMS.

Its an interesting experience, but conceptually I have concerns about a pack using hundreds of separate cells in close proximity. Eack of the parallel layers has 99 individual cells. These are not separately monitored and are spotweled to a common plate at both ends. You can never tell if a single cell goes bad. Possibly if there is a failure in a layer. I have another with similar 10+v and I am convinced that this also has one of the 99 cells in one of the parallel layers thats gone short circuit.
At something like $1800+ for each 12v nominal unit, this could be totally compromised by the failure of a single cell internally. None of which are servicable of accessible.
For me this shows I would only consider investing in Single Prismatics, which if any failure is exhibited can be swapped out and dont waste the rest of the pack.
A lot of the cars coming along use packs built like this.
On EV TV they had one of the Genuine A123 packs, that had a single cell failed, its also impossible to service. Vehicle Manufacturers will have to address servicability issue, as once they get into used market, the high cost of a genuine pack will mean 2nd hand prices of cars will drop like a stone. There is a potential market for companies offering to repair and remanufacture whole vehicle packs in the forthcoming years.

Grumpy-b

Spot welding permanently has been absolutely the issue with A123 packs. They are built to be unserviceable. It's costing them millions!

JR had two bad cells. One was basically dead the other was very poor. his moulded packs Must get hot inside. Tesla has cells with a fitted a ptc resistor.. This temperature problem is seemingly central to the troubles all cells have.

Gregs idea of the round cells is good because all cells with high C rates most seem have a lot of external area to lose the heat. Their plastic spacer blocks don't keep them close together but this ruins the density and makes for a big pack.

You say 4A charger, wondering, was it not fused?